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Leaf clip on chimpanzee vocalization during alpha takeover

Penelitian - Non-human primates accumulate gestures, facial expressions, and vocalizations in various ways to communicate effectively. Scientists from the Max Planck Institute for Evolutionary Anthropology in Leipzig report to PeerJ where chimpanzees (Pan troglodytes verus) use new tool signals when alpha men take over the leadership.

Two researchers reported a signal of leaf clippings that resurfaced in wild chimpanzees during alpha takeover at Taï forest in Côte d'Ivoire. This movement is only produced by adult male chimpanzees that precede vocalization and is associated with acoustic changes in the call.

"This is a rare example of the use of tools in a communicative context and has been proposed to be a culture that varies in meaning within different chimpanzee social groups," says Ammie Kalan.

Kalan and Christophe Boesch became the first researchers to report how leaf clip movements and vocalizations were associated with acoustic changes in calls within the chimp's communication complexity. Detailed acoustic analyzes of vocalizations and behavioral observations show that leaf clippings increase acoustics in drum beats and lower frequencies.

"We can not confirm the exact mechanism because leaf clippings did not occur at the same time but immediately before that. We think the leaf clippings may reappear in this group because of the passion and high aggression in the group during the peak time of the competition," Kalan said.

The researchers also noted the males looked socially frustrated and stressed during this period of instability hierarchy where leaf clippings may have helped alleviate some of these effects. Kalan and Boesch suggest opening this phenomenon further to other chimpanzee groups and examining the associated mechanisms.

"Often, chimpanzee males in Taï combine drums in which individual vocal and physical vigor are demonstrated.The male display is most likely an important signal to maintain competition during periods of hierarchical instability. Leaf clippings reappear in this group," Kalan said.

"This study adds to our understanding of the complex nature and multilevel communication in wild chimpanzees, especially the combination of signals, movement and vocalization as a powerful way to gain communicative flexibility," Kalan said.